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Man With Binoculars

If you have any additional questions about binoculars for bird watching which are not answered here then please get in touch with us via our contact form.

What do the numbers mean?

The two numbers that are part of the description of all binoculars are the magnification and the objective size.

The first number is the magnification or power of the binoculars and tells you how much larger an object will appear compared to viewing with the naked eye. So for 10x binoculars the object will appear 10x larger than usual.

If this number is actually two numbers then the binoculars are zooms or have variable power. The second number is the size in millimetres of the objective lenses or the aperture and gives an indication of how much light your binoculars take in. A bigger number will mean distant images should appear clearer and brighter.

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What are coated optics?

Coatings are layers of material added to the glass surface to improve the performance of optics by increasing the amount of light that passes through the lens into the eye.

If optics are not coated then up half the light that enters the objective lens will be lost so good coatings mean that a smaller objective can be used which results in a smaller, lighter pair of binoculars.

Be aware that for binoculars to be described as ‘coated’ they only need to have a single level of magnesium fluoride on one lens.

Multi-coated optics have more than one layer of coatings applied to at least one lens, whereas fully multi-coated optics will have up to 25 layers of coatings applied to all lenses. You will tend to find fully multi-coated optics only on premium binoculars.

What is the exit pupil?

The exit pupil is a virtual aperture and the bright spot of light that you can see when you hold your binoculars with the objective lenses pointed towards a bright light.

A larger exit pupil is required if you use your binoculars in low light but for bird watching during the day a smaller exit pupil will produce brighter images.

To calculate the size of the exit pupil divide the objective size by the magnification. So for 8 x 42 binoculars the exit pupil is 5.25 mm.

What do BK7 and BAK4 mean?

BK7 and BAK4 describe the type of glass used for the prisms. BK7 stands for borosilicate and BAK4 stands for barium crown.

BAK4 is generally more expensive than BK7 and produces sharper and brigher images. With prisms made from BAK4 binoculars can have a perfectly round exit pupil, whereas with BK7 prisms there will be some distortion around the outer edges.

What is the Field of View?

The Field of View (FOV) is the width of the image seen through your binoculars.

The FOV can be expressed as the width in feet at 1,000 yards– the linear field – or in degrees. – the angular field. To convert the linear field to get the angular field divide by 52.35.

For example a field of view of 300 feet at 10,000 yards means that if your binoculars are focused on an object 1,000 yards away the width of the image that you can see through the binoculars would be 300 feet. The angular FOV in that case would be 5.7 degrees.

Binoculars with wide FOVs make it easier to find and track objects , particularly if they are moving so are ideal for bird watching. However, be aware that a high FOV will mean a smaller magnification.

What is the difference between porro-prism and roof-prism?

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Can I use zoom binoculars for bird watching?

Zoom binoculars are binoculars with variable magnification and they are not usually recommended for bird watching.

Although they can be used at low power and you can ‘zoom’ in on a bird to see more detail the picture does not tend to be as clear as that of single magnification binoculars and they are prone to developing faults.

What binoculars should I buy if I wear glasses?

If you wear glasses you should buy a pair of binoculars with longer eye relief which will allow room for your glasses. Ideally you should look for a minimum of 15 mm.

Many people who wear glasses find the they don't need them when they are using binoculars unless your glasses are for correcting astigmatism as the focus range of binoculars can usually provide the same correction as your glasses.

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How do I clean my binoculars?

You should clean your binoculars gently and carefully in order not to damage the lenses or get water into the casing.

You can find out the best way to clean your binoculars here.

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Will I need a tripod for my binoculars?

Although you can use most binoculars without a tripod for bird watching, if you have a pair of binoculars with particularly high magnification, then you will need a tripod to ensure a steady image.

Binoculars over 12x magnification tend to be used in astronomy and if they are hand-held will result in a shaky picture. You can buy adapters for tripods for most makes of binoculars.


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